The ability to recognize and respond to environmental stress is an essential characteristic of all living organisms. A low oxygen state, or hypoxia, is an environmental stress encountered under physiological as well as pathophysiological disease states such as myocardial infarction and stroke. In higher eukaryotes, the cell-intrinsic transcriptional hypoxia response includes actions mediated by Hypoxia Inducible Factor (HIF) transcription factors. In vertebrates, the HIF family is comprised of three members with HIF-1 and HIF-2 being essential for survival as indicated by results from genetic ablation studies in mice. Despite their similarity at the protein level, HIF-1 and HIF-2 have distinct biological roles. HIF-2 is the specific HIF factor responsible for induction of erythropoietin and of major antioxidant enzymes (AOE) in adult mice, thereby regulating cell survival and protective cellular responses against oxidative stress, respectively. We recently demonstrated that HIF-2, but not HIF-1, signaling during hypoxia is selectively augmented by Sirtuin 1 (Sirt1), a deacetylase also implicated in aging, nutrient sensing, and genotoxic stress response. Our central hypothesis is that Sirt1/HIF-2 signaling is an essential signaling pathway for protection against hypoxia-induced damage in mammals. Preliminary data within this proposal reveal that Sirt1 levels increase during hypoxia, HIF-2 is acetylated by specific cellular acetyltransferases during hypoxia, and cardiomyocyte-specific HIF-2 ablation in mice results in worse outcome following myocardial infarction. The experiments proposed are aimed at elucidating the mechanism and biological role for Sirt1/HIF-2 signaling in mammals using test tube, cell culture, and animal model studies. Our long-term goals are to identify the prosurvival mechanisms activated during hypoxia and to leverage this knowledge to develop novel therapeutic agents for treatment of myocardial infarction and stroke, the leading causes of morbidity and mortality in US adults today. The Specific Aims of this proposal are as follows: Aim 1: Define the role of HIF signaling in Sirt1 activation during hypoxia Aim 2: Define the role of acetylation in Sirt1/HIF-2 signaling Aim 3: Define the role of HIF-2 in cardiac physiology after myocardial infarction PUBLIC HEALTH RELEVANCE: A low oxygen level is a major feature of several human diseases including heart attack, stroke, and cancer. When faced with this stress, cells in our body respond by turning on genes in an attempt to survive. Understanding how this response is controlled will allow us to design new drugs that will save cells (as desired after a heart attack or stroke) or to kill cells (as desired in the case of cancer).